High-purity (SupT) and reagent-grade (ST), stoichiometric and silicate-containing a-tricalcium phosphate (alpha-TCP: STO/SupTO and Si-TCP x = 0.10: ST10/SupT10) were prepared by solid-state reaction based on the substitution mechanism Ca-3(PO4)((2-x))(SiO4)(x). Samples were determined to be phase pure by X-ray diffraction (XRD), and Rietveld analysis performed on the XRD data confirmed inclusion of Si in the alpha-TCP structure as determined by increases in unit cell parameters; particularly marked increases in the b-axis and beta-angle were observed. X-ray fluorescence (XRF) confirmed the presence of expected levels of Si in Si-TCP compositions as well as significant levels of impurities (Mg, Al and Fe) present in all ST samples; SupT samples showed both expected levels of Si and a high degree of purity. Phosphorus (P-31) magic-angle-spinning solid-state nuclear magnetic resonance (MAS NMR) measurements revealed that the high-purity reagents used in the synthesis of SupTO can resolve the 12 expected peaks in the P-31 spectrum of a-TCP compared to the low-purity STO that showed significant spectral line broadening; line broadening was also observed with the inclusion of Si which is indicative of induced structural disorder. Silicon (Si-29) MAS NMR was also performed on both Si-TCP samples which revealed Q(0) species of Si with additional Si Q(1)/Q(2) species that may indicate a potential charge-balancing mechanism involving the inclusion of disilicate groups; additional Q(4) Si species were also observed, but only for ST10. Heating and cooling rates were briefly investigated by P-31 MAS NMR which showed no significant line broadening other than that associated with the emergence of beta-TCP which was only realised with the reagent-grade sample STO. This study provides an insight into the structural effects of Si-substitution in alpha-TCP and could provide a basis for understanding how substitution affects the physicochemical properties of the material. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Bibliographical noteOpen Access funded by Engineering and Physical Sciences Research Council
- stabilized calcium phosphates
- in-vivo behavior
- hydroxyapatite granules
- powder diffraction